Art of cracking hydrocarbon oils



March 23 1926.

E. W. ISOM ART OF GRACKING HYDROGARBON OILS Filed June 19, 1925 2 Sheets-Sheet l NG Qwm Il' N III WS@ 5km INVENTOR Edward W /50/72 QQ/Www ATTORNEYS E. W. ISOM ART OF GRACKING HYDROGARBON @ILS March Z3 1926 Filed June 19, 1925 2 Sheets-Sheet 2 PatentedMar. 23, 1926.

UNITEDI STATES EDWARD W. ISOM, OF LOCUST VALLEY, NEW YORK, ASSIGNOR' TO SINCLAIR REFIN`- PATENT OFFICE.

ING COMPANY,'OF NEW YORK, N. Y., A CORPORATION OF MAINE. I

Aar or CRACKING HYnnocARBoN onfs.

Application -led J'une 19, 1925. Serial No. 38,128.` Q v To all whom t may concern.'

Be it known that I, EDWARD W. IsoM, a citizen of the United States, residing at Locust Valley, in the county of Nassau, State of New York, have invented certain new and useful Improvements in the Art of Cracking Hydrocarbon Oils; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as Will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to improvements. in the cracking of heavier hydrocarbon oils, such as gas oil or kerosene, to produce lighter hydrocarbon o-ils, such as gasoline or pressure distillate, therefrom. This application is in part a continuation of my prior application filed August Q8, 1922, Serial No. 584,711.

The invention relates particularly to improvements in the construction and operation of externally heated tubular single pass oil cracking stills or in cracking still systems in which externally heated tubular single pass heaters are employed. The invention includes improvements in both method and apparatus.

When hydrocarbon oils are heated to a cracking temperature, they are decomposed with the formation of lighter hydrocarbon oils. The products of the cracking reaction also include a certain amount of fixed gases and heavy tar or pitch or carbon. When the cracking isv effected by external heat transferred to the oil through the walls of heating tubes, the carbon or tarry matter tends to deposit on the heating surfaces in contact with the oil and to form an insulating layer thereon which retards heat transfer. Not only does this deposit impede the effective transfer of the heat to the oil, but it also deprives the Walls of the heating tubes of the protective effect of the oil which tends to reduce the temperature of the tube Walls by absorbing heat therefrom. The result is a tendency toward increase in temperature. of the tubes, as compared to the oil passing therethrough which accelerates the deposition and tends to bake the deposit toa dense closely adherent mass further increasing the temperature of the tubes. This tendency imposes a danger of rupture due to overheating and is usually the limiting factor both in the life of the heating tubes as Well as inthe period over Which the operation can be continued in a single run. The heating tubes nearest the fire-box and first exposed to the fresh productsl of combustion are subljected to the most severe conditions, and the most easily cracked oils tend to cause the greatest deposit of carbonaceous material under any given conditions. The rate of deposition with any one oilcalso increases oil cracking stills or heaters, the oil is passed but once thro-ugh the oil heating tubes and the entire heat input to the oil is effected in a single passage of the oil through 'the heating tubes, the oil supplied to the still being brought from its initial temperature to the desired cracking temperature in the single passage lof the oil through the heating tubes. In referring to single pass heaters, I refer to stills in which fresh oil is circulated but once through the oil heating tubes and include stills Where vaporized fractions of the oil are refluxed and recirculated through the heating tubes,`but I exclude stills in which the fresh oil itself or any unvaporized portion thereof is recirculated through the heating tubes. In such stills it is desirable, for efficiency of operation and economy of equipment, to transfer the maximum amount of heat to the oil in a minimum distance of oil travel, and at the same time' to avoid overheating o-f the still tubes and other severe strains on the still equipment. Hithereto, these apparently contrary factors have prevented development of maximum heating elliciency in externally heated single pass tubular oil cracking stills. For example, proposals have beenmade to use `relatively 10W furnacel temperatures reducing the temperature of the hot products of Aa new method of operating cracking stills of this general character in which the heating tubes are protected While high heating etliciency is secured. The invention also provides an improved way of handling refiux in externally heated single pass tubular cracking stil s. @ther features and advantages will appear as the description proceeds. Y

According to the `present invention, the vapors of the cracked oil discharged from the single pass heater are subjected to a retluxing operation and the reflux therefrom is circulated through the tubes of the heater, fresh oil being supplied to the heater at an intermediate point, and the' hot products of combustion from'the lire-box are circulated overpthe tubes of the heater in generally concurrent relation with the oil iow. The heating gases thus first contact with the heating tubes through which the refluxed oil is "circulating and then contact, after be- Y ing reduced in temperature by the heat absorption on these initial tubes, with the heatingv tubes through which the fresh oil iscirculating in admixture with the reflux. The redux is relatively refractory and assists in tempering the heating gases without excessive carbon formation and at the saine time is subjected to high temperatures which assist in cracking it with the productiony of the desired lighter products. rl`he fresh oil is then subjected td the milder heating action of the tempered heating gases, andthe hot products discharged from the initial heating tubes into the heating tubes lthrough which the fresh oil is circulated also assist in heating the fresh voil internally .as admixed therewith. rllhe initial heating tubes are thus employed to temper the heating gases while they are protected by circulation of relatively re ractory stock therethrough and the -lattertubes are protected by this tempering of the heating gases. A. part of the heating gases escaping from the heating furnace may be recycled over'the heating tubes with the fresh products of combustion to further assist in protecting the heating tubes and improving the cracking operation. The single pass heater may be arranged to discharge into a vaporizing chamber or Yreservoir, which may be heated externally or which may be heated -internally only by the hot productsdischarged from the single pass heater, and to which additional fresh oil may or may not be supplied.

rllhe invention will be further describedl in connection with the accompanying drawings which illustrate in a diagrammatic and conventional manner apparatus embodying the invention and adapted for carrying out` the invention, but it is intended and will be understooa that this further description una illustration are for the purpose of exemplification and that the invention is not limited thereto.

- in elevation and partly in section, one form of apparatus embodvinglthe invention and adapted for carrying out the process of the invention, and

. Fig. 2 is a diagrammatic illustration of the process and of the operation of the apparatus ofthe invention in the nature of a How sheet.

lin the drawings a single pass ,externally heated tubular still is shown dschar ing into a. shell still ora reservoir from wiich v apors of the cracked oil are taken olf. 'lhe single pass heater comprises a furnace 1 in which a battery of heating tubes are arranged. 'llhe battery is made up of two sets of tubes, 2 and 3, connected at 4. A connection 5 is arranged for supplying oil to the set of tubes 2 whence it is discharged into the Set of tubes 3 through connection ll, L

another connection 6 being arranged for supplying oil` at this intermediate point.

After passing throughthe battery of heating tubes in a single pass, the oil supplied through connections 5 and 6 is discharged into the reservoir 8 through connection 7.

The heating furnace 1 is provided with a i lire-box 9 and a stack flue 10,'heating gases being circulated from. the fire-box first. over the set of tubes 2 and then over the set of tubes 3 to the stack Hue. r1`he {ire-box is provided With means for burning the fuel employedto supply the heat used in the cracking'operation. A burner for gaseous or liquid fuel is shown at 11. 'A return connectionv 12 provided withV forcing means' 13 lis arranged for withdrawing heating gases from near the outlet to the stack flue and recycling them over the oil heating tubes in.

through connection 14 and pass successively through two reflux towers 15 and 16'and thence to a condenser 17. rl`he distillate is condensed in the condenser and discharged into the receiver 18, whence condensate is drawn off through connection 19 and uncondensed vapors and v gases through connection 20. ln the redux, towers the reflux tower 15 in indirect heat exchanging relation with the vapors therein from connection 21 by means of pump 24k and is introduced into the shell or reservoir through connection 25. Excess oil forv cooling may be so pumped through tower 15 and the excess discharged through connection 26. ln thisv way vthe reduxing operation may be regulated. The redux tower 15 may however reo' ' lighter products,

be omitted. Fresh oil to be supplied to the single pass heater is pumped through the reflux tower 16 from connection 23 by means of pump 27 and is then'introduced into the single pass heater at an intermediate point through connection 6. The reflux from the tower 16, and from the tower 15 if employed, flows to the tank 28 where it is introduced into the first set of tubes12 through connection 5 by means of pump 29. Additional oil may also besupplied tothe first set of tubes through connection 22.

In operation a stream of oil is forcedun'a single pass through the heating condiut 1n the heating furnace. Initially this stream is made up of refluxed oil and the fresh heat-l ing gases at highest temperature are first brought into contact with that part of the conduit through which the reflux 1s circuy lating. The heating gases are thus reduced in temperature bythe heat obsorbed 1n this part of the conduit while at the same time this part of the conduit exposed to the most severe lconditions is protectedby the absorption of heat in the relatively refractory reflux. Likewise, the relatively refractory reflux is here subjected to cracking conditions adapted to decompose it into the deslred and other more lor less refractory stocks may also be supplied to this part of the heating conduit with the reflux. Fresh oil is then supplied to the stream at an intermediate point and the heating isl continued by vheat exchangewith they tempered heating gases. As fresh oil issupplied to the stream it is in part heated by admixture with the reflux andthe cracked reflux constituents and as this heat is supplied linternally it does not increase the tendency to deposition. The lwalls of the latter part of the conduit are thus further protected.bybeing relieved of the burden of transferring` the heat so supplied. By preheating` the fresh oil, for Vexample by heatexchange with the cracked vapors, the heating tubes are further protected by' relief from another i part of the heating burden. The reflux'may j also be 'returned to the heating conduit at a;

relatively high temperature. With the same' size vheating tubes, the rate of flow is 'in-v creased as the yvolume of oil and cracked products flowing through the heatingr conduit increases. This may'however be regulated by 'adjusting the relative size-of theheating tubes. The operation of the single' pass heater as just described, aswell as the operation of the remainder of the apparatus illustrated in Fig. 1,' is pictorially represented in Fig. 2. e

- In the apparatus illustrated, the heating conduit discharges into a vaporizing drum or reservoir in which the vapors of. the,

crackedoil are separated from any residue. The residue may be" reduced to cokein this reservoir or ltmay be withdrawn. asa flux oss 8 be supplied to the vaporizingdrum, but it may advantageously be heated internally only by the hot products discharged from the single pass heater. The temperature through connection '30. External heat may conditions in the reservoir may also be regulated by supplying fresh oil thereto. Where the reservoir is heated internally only, or where ,only a small amount of heat is supplied externally for example enough to make up for radiation losses, more easily cracked oils may advantageously be cracked therein by the heat supplied by the hot products discharged from the single pass heater. The apparatus illustrated is also flexible as to pressure control. The pressure in the single pass heater may exceed that in the reservoir by just sufficient to maintain flow theref ,through at the desired rate, or a substantially higher pressure may be maintainedin the heater. The pressure may also be reduced between the reservoir andthe reflux towers or they may be operated in open communication. The pressure may also be reduced between the reflux towers and the con` denser, or the pressure may be maintained through the condenser and reduced at a point beyond the condenser. The actual pressures employed may vary widely. In the heater, pressures of from about 25 up to 300pounds e per square inch or more-may be employed and a similar range of pressures may be used inthe reservoir. I

Another advantage of the invention is that` it provides an apparatus and a `method of operation in which a series of zones are provided in l'which cracking conditions of progressively decreasing rigor are maintained, `and advantage may be taken of ,this feature of the invention in handling charging stocks of diEerent character. In the f production of gasoline in apparatus of the type illustrated, for example, the fresh o-l supplied to the heating conduit at the intermediate point may be-.of a gas oil or kerol sene character. The reflux initially supplied to the heating conduit will comprise the vaporized constituents heavier than suitable as components of the desiredpressure distillate. Other light oils may also be initially supplied to the heating conduit in vadmixture with the reflux, for .example` where a gas oil charactergstock is supplied t'o the conduit at an intermediate point a kerosene, or lightikerosene., character stock may besupplied in admixture with the reflux. kHeavy or easily cracked stocks may with .advantage be supplied lto the reservoir. For example, a'heavy gas oil -maybe supplied to the reservo1r. Pressure' still tar or topped crude oils may also be introduced into the reservoir 'and cracked thereinffby the heat of the hot products discharged l from the single pass heater.

In the' production ofgasolineor pressure distillate from charging stocks such as those' charged from the single pass heater is in the neighborhood of from about 700 to 1200o F. Where no heating gases are recirculated, the temperature of the fresh heating gases first contacting with the tubes may be as high as 2100o to 27000 F. Where part of the heating gases are recirculated, for example as more particularly described in my application filed May 15, .1925, Serial No. 30,404 the temperature of the heating gases as they first contact with the tubes may be reduced, for example to something in the neighborhood of 900 to 1500o F., While the efficiency of the operation is nevertheless maintained. By combining recirculation of part of the heating gases with the improved way of supplying fresh oil and reflux to the single pass heater, as is contemplated in one aspect of the invention, the heating tubes ofrthe single pass heater are further protected while providing an ing operation to the conduit at a point adA improved and efficient cracking operation.

f claim:

1. An improved method of cracking hydrocarbon oils, which comprises circulating oil in a single pass through a heating conduit, heating the oil circulating through the conduit to a cracking temperature by circulating heating gases thereover in generally concurrent relation with the oil flow, subjecting the vapors of the cracked oil dis-P charged from the conduit to a reiuxing operation, supplying reflux from the refluxjacent the end of vthe conduit over which the heating gases rst circulate, and supplying fresh oil tothe conduit at an intermediate point.

An improved method of cracking hydrocarbon oils, which comprises circulating oil in a single pass through a heating conduit, heating the oil circulating through the conduit toA a cracking temperature by circulating heating gases thereover in generally concurrent relation with the oil llow, subjecting the vapors of the cracked oil discharged from theconduit to a reluxing operation, supplying reflux from the refluxing operation to the conduit at a point adjacent the end of the conduit over which lthe heating gases, firstv circulate,

supplying fresh .oil to the conduit at an intermediate point, 'and recirculating over the heating conduit part vof" the heating gases which havepassed thereover in admiirture, with fresh heating gases. ,60 j drocarbon oils, which comprises circulating 3. Anl improved method of cracking voil in a single vpass through a' heating conduit, heating the oil circulating through the conduit to a cracking temperature by circulating heating gases thereover in generally charged from the conduit toa reliuxing operation, supplying refluxv from the. reluxing operation to the conduit at a point adjacent the end of the conduit over which the heating gases first circulate, preheating fresh oil, and supplying the preheated fresh oil to the conduit/at an intermediate point.

4. Animproved method of cracking hydrocarbon oil, which comprises i circulating oil in a single pass through a hea-ting conduit and thence into -a reservoir, heating the oil circulating through the conduit to a cracking temperature by circulating heating -gases thereover in generally concurrent rela-- tion with the oil lw, taking olf vapors of the cracked oil from the reservoir and subjecting them to a retluxing operation, supplying reflux from the refluxing operation to the conduit at a point adjacent the end of the conduit over which the heating gases first circulate, and supplying fresh oil to the conduit at an intermediate point. j'

5. An improved method of cracking hydrocarbon oil, which comprises circulating oil in a single pass through a heating conduit and thence into a reservoir, heating the oil circulating through the conduit to la cracking temperature by circulating heating gases thereover in generally concurrent relation with the oil flow, taking off vapors of f arranged therein; a `reflux tower communiv eating with the discharge end of the heating conduit, means for supplying reux from the said tower to the inlet end of the conduit, means for supplying fresh oil to the conduit at an intermediate point, and a firebox communicating with the furnace at a point adjacent the supply end of the heatmg conduit. i

7. An improved apparatus for cracking hydrocarbon oils, which comprises' a heating ffurnace and a single pass heating conduit arrangedftherein. a. reflux tower communieating with the discharge end of the heating I conduit, means for supplying reflux from the said tower to the inlet end of 'the conduit, means for supplying fresh oil to the conduit at an intermediate point, a fire-box communicating with the furnace at a point adjacent the supply end of the heating cong duit, and means for recirculating heating hydrocarbon oils, which com rises a heating furnace, a reservoir, a singe pass heating -conduit arranged in "the furnace/and arranged to dischargel into the reservoir, V a reflux tower communlcating` with the vapor space ofthe reservoir, means for supplying heating conduit opposite the discharge end,

. means for' supplying fresh oil to .the conduitJ at an' intermediate point, and a fire-box com- -mimica-ting with the furnace at a point adjacent the supply end of the heating conduit. 9 improved apparatus fOrf cracking hydrocarbon oils, which comprises a heating furnace, a reservoir, a single pass heating conduit arranged in the furnace and arranged to discharge into the reservoir, a

reflux tower communicating with the vapor space of the reservoir, means for supplying reux from the said tower to the end of the heating conduit opposite the discharge end, means foil-'supplying fresh oil to the conduit at an intermediate point, a fire-box com'- municatingwith the furnace at a.point 'adjacent the supply end of the heating conduit, and means for recirculating heating gases escaping from the furnace again over the heating conduit.

In testimonywhereof I affix my signature.

" EDWARD W. ISOM. 

